Filter cartridge with strap and method

ABSTRACT

A filter cartridge ( 20 ) for removing particulates from a particulate laden fluid stream moving one direction through the filter cartridge. The filter cartridge ( 20 ) is periodically subject to cleaning fluid moving in an opposite direction to the fluid stream. The filter cartridge ( 20 ) comprises filtration media ( 24 ) formed into a tubular configuration and having a plurality of circumferentially spaced apart pleats ( 26 ). A retention device ( 82 ) to limit radial movement of the filtration media ( 24 ) when subjected to the periodical cleaning fluid and to maintain the pleats ( 26 ) in the filtration media circumferentially spaced apart. 
     A method of making a filter cartridge ( 20 ) for removing particulates from a fluid stream moving one direction through the filter cartridge and that is periodically subject to cleaning fluid moving in an opposite direction to the fluid stream. The method comprises the steps of providing filtration media ( 24 ) formed into a generally tubular configuration and having a plurality of circumferentially spaced apart pleats ( 26 ). A retention device ( 82 ) is applied to limit radial movement of the filtration media ( 24 ) in the opposite direction when subjected to the periodic cleaning fluid and to maintain the pleats ( 26 ) in the filtration media circumferentially spaced apart.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to a filter cartridge. Inparticular, the present invention relates to a retention strap for thefilter cartridge and method of manufacturing the filter cartridge withthe retention strap.

2. Description of the Prior Art

Filter cartridges that have pleated filtration media for filteringparticulates from a particulate laden fluid stream moving in onedirection through the filter cartridge are known. Such a filtercartridge is often subjected to cleaning fluid pulses moving for shortperiods of time through the filtration media in a direction opposite tothe direction that the particulate laden fluid stream moves. Such afilter cartridge is referred to as a “pulse pleat” filter cartridge.Known retention straps encircle portions of the pulse pleat filtercartridge to prevent the filtration media from excessive movement duringexposure to the cleaning fluid pulses.

However, the known retention straps for pulse pleat filter cartridgeshave drawbacks because they are difficult to install onto a filtercartridge and may not remain in the relative axial location they areinitially placed in. For example, a known textile retention strap mustbe manually wrapped about the filtration media of the filter cartridge.The textile retention strap is typically tightened manually and the endsof the retention strap are overlapped. The ends of the retention strapare then adhered or fastened together while a desired tension ismanually maintained on the retention strap.

It is important that the retention strap remain in a desired relativeaxial location along the filter cartridge to assure that the strapproperly protect the filtration media from excessive movement duringexposure to the cleaning fluid pulses. This is typically accomplished bythe use of an adhesive. However, such an adhesive axial location devicehas been known to fail and the strap may become incorrectly positionedaxially along the filter cartridge.

SUMMARY OF THE INVENTION

The present invention is directed to a filter cartridge for removingparticulates from a particulate laden fluid stream moving one directionthrough the filter cartridge. The filter cartridge is periodicallysubjected to cleaning fluid moving in an opposite direction to thedirection the particulate laden fluid stream moves. The filter cartridgecomprises filtration media having a plurality of pleats. The filtrationmedia is formed into a tubular configuration and has a plurality ofcircumferentially spaced apart pleats. Mounting structure is at a firstaxial end portion of the filtration media. An end cap is at a secondaxially opposite end portion of the filtration media. The filtrationmedia is maintained in the generally tubular configuration by themounting structure and the end cap. A retention device limits radialmovement of the filtration media when subjected to the periodic cleaningfluid and maintains adjacent pleats in the filtration mediacircumferentially spaced apart.

The retention device comprises a thermoplastic elastomer materialcapable of withstanding the elevated operating temperatures andoperating environment that the filter cartridge is exposed to. Theretention device is attached to the filtration media. Each of the pleatsof the filtration media has a tip and a pair of sides extending from thetip. The retention device engages and is adhered to at least one of thetips and sides of pleats of the filtration media. The retention deviceis applied to the filter cartridge during an extrusion operation. Theretention device further includes reinforcement structure.

The present invention is also directed to a method of making the filtercartridge. The method comprises the steps of providing filtration mediaformed into a tubular configuration and having a plurality ofcircumferentially spaced apart pleats. Mounting structure is provided ata first axial end portion of the filtration media and an end cap at asecond axially opposite end portion of the filtration media to maintainthe filtration media in the generally tubular configuration. A retentiondevice is applied to limit radial movement of the filtration media inthe opposite direction when subjected to the periodical cleaning fluidand to maintain the pleats in the filtration media circumferentiallyspaced apart.

The retention device applying step further includes the step ofproviding a thermoplastic elastomeric material capable of withstandingthe elevated operating temperatures and operating environment that thefilter cartridge is exposed to. Each of the pleats of the filtrationmedia has a tip and a pair of sides extending from the tip. The methodalso includes attaching the retention device to the filtration media.The retention device applying step further includes providing aretention device that engages at least one of the tips and sides ofpleats of the filtration media. The retention device applying stepfurther includes the step of extruding the retention device onto thefilter cartridge. The extruding step further comprises the step ofholding and rotating the filter cartridge while applying the retentiondevice directly onto the filter cartridge. The retention device applyingstep further includes the step of providing reinforcing structure in theretention device. The providing reinforcing structure step furtherincludes the step of extruding the retention device on to the filtercartridge. The method also includes the step of deforming a portion ofthe retention device between adjacent pleats.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention will become apparent to thoseskilled in the art to which the present invention relates from readingthe following description with reference to the accompanying drawings,in which:

FIG. 1 is a perspective view of a filter cartridge incorporating aretention strap embodying the present invention;

FIG. 2 is a side elevation view of the filter cartridge in FIG. 1;

FIG. 3 is a cross-sectional view of the filter cartridge in FIG. 2,taken approximately along the line 3—3 in FIG. 2;

FIG. 4 is a view similar to FIG. 3 illustrating an alternate embodimentof the invention;

FIG. 5 is a side elevation schematic illustration of the extrusionequipment and one embodiment of the process used to apply the retentionstrap to the filter cartridge; and

FIG. 6 is a schematic illustration of the extrusion equipment andprocess illustrated in FIG. 5, viewed from above.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is embodied in a filter cartridge 20 (FIGS. 1 and2) for removing particulates from a particulate laden fluid streammoving one direction through the filter cartridge. The filter cartridge20 is particularly suitable for use in air pollution controlapplications. The filter cartridge 20 is a “pulse pleat” type of filtercartridge that is periodically subject to pulsed cleaning fluid movingin an opposite direction to the direction that the particulate ladenfluid stream moves, as is known. Such a filter cartridge 20 may besubjected to over 300,000 cleaning pulses per year over a typicalexpected service life of about two years. The filter cartridge 20 isoperably attached to a tube sheet 22 (FIG. 2) in a plenum (not shown) ofa known baghouse (not shown).

The filter cartridge 20 includes filtration media 24 that is formed intoa generally tubular or cylindrical configuration, as illustrated inFIGS. 1 and 3-4, with a longitudinal central axis A. The filtrationmedia 24 has a plurality of pleats 26 which are circumferentially spacedabout the circumference of the filter cartridge 20. Each pleat 26 has atip 42 formed at its radially outermost location, as viewed in FIGS. 1and 3-4, and a pair of sides 44 extending radially inward from the tip.The pleats 26 in the filtration media 24 are not necessarily stiff andstrong, thus, the pleats are prone to radially outward movement during acleaning fluid pulse. Excessive radial outward movement of thefiltration media 24 can damage the filtration effectiveness of thefilter cartridge 20. Adjacent pleats 26 may also “collapse” andtemporarily engage one another during a cleaning pulse or during afiltration cycle. When adjacent pleats 26 engage one another, there is achance that the cleaning pulse or filtration operation will not be aseffective as it should be because gas flow through that portion of thefiltration media 24 can be temporarily blocked. Thus, it is desirable toprevent excessive radial movement of the filtration media 24 andcollapse of the pleats 26.

Mounting structure 62 (FIGS. 1-2) is located at a first axial endportion of the filtration media 24 and filter cartridge 20. The mountingstructure 62 is made of an elastomeric material for mounting and sealingthe filter cartridge 20 in an opening 64 (FIG. 2) in the tube sheet 22.A known suitable material for the mounting structure 62 is preferablymade from a molded urethane material. An end cap 66 is located at anaxially opposite second axial end portion of the filtration media 24 andfilter cartridge 20. The end cap 66 is preferably made from a moldedurethane material. The filtration media 24 is potted and maintained inthe generally tubular configuration by the mounting structure 62 and theend cap 66. A permeable support 68 is located radially inward of thefiltration media 24 to prevent inward collapse of the filtration media24 during exposure to the particulate laden fluid stream that is to befiltered.

The filter cartridge 20 also includes a retention device in the form ofa plurality of retention straps 82, constructed according the presentinvention. The retention straps 82 limit radial movement of thefiltration media 24 in the radially outward direction, opposite to theflow of the fluid stream to be filtered, when subjected to theperiodical cleaning fluid. The retention straps 82 also serve to spaceapart and maintain adjacent pleats 42 spaced apart around thecircumference of the filter cartridge 20.

Each retention strap 82 embodying the present invention is preferablymade from a thermoplastic elastomeric material having sufficientstrength and fatigue resistance to prevent excessive radial movement ofthe filtration media 24 during a cleaning pulse and maintain the pleats26 spaced apart. The retention strap 82 is also capable of withstandingthe elevated operating temperatures and operating environment, such asexposure to moisture and chemical degradation, that the filter cartridge20 is typically exposed to and designed for. The retention strap 82 canbe made from any suitable material. Particularly suitable materials havebeen found to be Hytrel® 5556 or 8238 thermoplastic polyester elastomeravailable from DuPont.

The material of the retention strap 82 is selected for its strength andimpact resistance at the relatively elevated operating temperatures thatthe retention strap will be exposed to. The material of the retentionstrap 82 is also selected for its resistance to chemical and moisturedegradation of its strength and impact resistance. The preferredthermoplastic polyester elastomer meets these design parameters.Incomplete testing has shown that the strap can withstand over 150,000cleaning pulses and function while constantly exposed to at least 265°F., and in some cases 350° F., without losing its strength and withoutmoving axially along the filter cartridge from the position it wasinitially placed in.

The retention strap 82 engages and is adhered to at least some tips 42and perhaps some of the sides 44 of pleats 26 of the filtration media24, as illustrated in FIG. 3. The engagement minimizes radially outwardmovement of the tips 42 of the pleats 26 and that the pleats aremaintained spaced apart without collapsing against one another duringexposure to the pressure and flow of the cleaning fluid or theparticulate laden air. The adherence assures that the retention strap 82remains in the relative axial location it was originally placed inthroughout its service life.

The retention strap 82 is preferably applied to the filter cartridgeduring an extrusion operation. The retention strap 82 is adhered to thefiltration media 24 during the extrusion operation so it does not movealong the filter cartridge in a direction parallel to the axis A. Duringthe extrusion operation, the retention strap 82 has portions 84 (FIG. 3)which are forced to extend at least partially into the region betweenadjacent pleats 26. This assures that there is some structure locatedbetween the pleats 26 that prevent adjacent pleats from engaging eachother. The retention strap 82 is also forced to engage and adhere totips 42 and/or sides 44 of the pleats 26 to assure that the retentionstrap remains in the axial position it was originally applied to thefilter cartridge 20. Once the material of the retention strap 82“cures”, it has a hardness and strength sufficient to withstand theoperating environment it will be exposed to for its service life andadheres to the filtration media 24.

The retention strap 82 according to an alternate embodiment of thepresent invention further includes reinforcement structure 86 (FIG. 4).The reinforcement structure 86 may be any suitable material but iscontemplated to be textile reinforcement. The reinforcement structure 86is introduced during the extrusion operation. The reinforcementstructure 86 may be introduced during a single extrusion pass and forcedinto the extrudate or introduced between two separate extrusion passes.

The present invention is also directed to a method of making a filtercartridge 20 with the retention strap 82, as illustrated in FIGS. 5 and6. The method includes an extruder 102, a pivotable application roller104, a cutoff mechanism 106 and an optional reinforcement applicator(not shown). The method of the present invention is described below.

A filter cartridge 20 without any retention device is held in proximityto the extruder 102 by a support mechanism 122. The support mechanism122 is adapted to hold and rotate the filter cartridge 20 during theapplication of an extruded retention strap 82. The support mechanism 122includes a mounting structure holder 124 and an end cap holder 126. Themounting structure holder 124 closely fits within and supports themounting structure 62 of the filter cartridge 20. The end cap holder 126supports the end cap 66 of the filter cartridge 20. The supportmechanism 122 positions the filter cartridge 20 so the longitudinalcentral axis A of the filter cartridge extends in a direction normal toa barrel 142 of the extruder 102. Either or both of the holders 124 or126 are operably connected with a drive mechanism (not shown) to rotatethe supported filter cartridge 20 under the barrel 142 of the extruder102, in a clockwise direction as illustrated by the arrow R in FIG. 5.

The filter cartridge 20 is rotated under the barrel 142 of the extruder102 while a band of extrudate 144 is applied to the outer surface thefilter cartridge 20. The application roller 104 is loaded to apredetermined force so the portions 84 of the uncured extrudate 144 isforced to deform in between adjacent pleats 26 of the filtration media24. The application roller 104 also forces the extrudate 144 to contacttips 42 and sides 44 of pleats 26 to engage and adhere the retentionstrap 82 to the filtration media 24. The extrudate 144 then is allowedto cure to form the retention strap 82.

In an alternate embodiment, reinforcement structure 84 may be introducedinto the retention strap 82. Textile reinforcement 84 is paid off theoptional reinforcement applicator. The textile reinforcement 84 isintroduced into the extrudate 144. The application roller 104 forces thetextile reinforcement 84 into the extrudate 144. Optionally the textilereinforcement 84 could be placed between two separate layers ofextrudate 144.

When circumferentially opposite ends of the extrudate 144 overlap, thecutoff mechanism 106 is activated to sever the extrudate 144. Theapplication roller 104 then creates a unified one-piece retention strap82 that remains in its axial relative place and supports the pleats 26and prevents engagement between adjacent pleats.

From the above description of preferred embodiments of the invention,those skilled in the art will perceive improvements, changes andmodifications. Such improvements, changes and modifications within theskill of the art are intended to be covered by the appended claims.

Having described at least one preferred embodiment of the invention,what is claimed is:
 1. An improved filter cartridge for removingparticulates from a particulate laden fluid stream moving in onedirection through said filter cartridge, the filter cartridgeperiodically subject to cleaning fluid moving in an opposite directionto the fluid steam, the filter cartridge including a filtration mediaformed into a tubular configuration with a plurality ofcircumferentially spaced apart pleats, mounting structure at a firstaxial end portion of the filtration media, and an end cap at a secondaxial end portion of the filtration media, the filtration media retainedin the generally tabular configuration by the mounting structure and theend cap; said improvement comprising: an extruded retention deviceengaging the filter cartridge to limit repeated radial movement of thefiltration media when subjected to the periodic cleaning fluid and tomaintain the pleats in the filtration media circumferentially spacedapart, and the retention device comprising a thermoplastic polyesterelastomer operable to limit repeated radial movement of the filtrationmedia at temperatures above approximately 265° F.
 2. The improved filtercartridge of claim 1 wherein said retention device is attached to thefiltration media to resist movement in direction parallel to alongitudinal central axis of the filter cartridge.
 3. The improvedfilter cartridge of claim 1 further including each of the pleats of thefiltration media having a tip and a pair of sides extending from thetip, wherein said retention device engages at least one of the tips andsides of the pleats.
 4. The improved filter cartridge of claim 1 whereinsaid retention device further includes reinforcement structure.
 5. Theimproved filter cartridge of claim 4 wherein said reinforcementstructure comprises textile material.
 6. The improved filter cartridgeof claim 1 wherein said retention device includes a portion extendingbetween adjacent pleats of the filtration media.
 7. A filter cartridgefor removing particulates from a fluid stream moving one directionthrough said filter cartridge, the filter cartridge periodically subjectto cleaning fluid moving in an opposite direction to the fluid stream,said filter cartridge comprising: filtration media formed into a tubularconfiguration; a plurality of circumferentially spaced apart pleats insaid filtration media; and an extruded retention device engaging thefilter cartridge to limit repeated radial movement of said filtrationmedia in the opposite direction when subjected to the periodicalcleaning fluid and to maintain said pleats in the filtration mediacircumferentially spaced apart, and the retention device comprising athermoplastic polyester elastomer operable to limit repeated radialmovement of the filtration media at temperatures above approximately265° F.
 8. The filter cartridge of claim 7 further including each ofsaid pleats of said filtration media having a tip and a pair of sidesextending from said tip, wherein said retention device engages at leastone of said tips and sides of the pleats.
 9. The filter cartridge ofclaim 7 wherein said retention device further includes reinforcementstructure.
 10. The method of claim 9 wherein said retention structurecomprises textile material.
 11. The filter cartridge of claim 7 whereinsaid retention device is attached to said filtration media to resistaxial movement along said filtration media.
 12. The filter cartridge ofclaim 7 wherein said retention device includes a portion extendingbetween adjacent pleats of the filtration media.
 13. A method of makinga filter cartridge for removing particulates from a fluid stream movingone direction through said filter cartridge and that is periodicallysubject to cleaning fluid moving in an opposite direction of the fluidstream, said method comprising the steps of: providing filtration mediaformed into a substantially tubular configuration and having a pluralityof circumferentially spaced apart pleats formed therein; and extruding athermoplastic polyester elastomer retention device onto the filtrationmedia to limit repeated radial movement of said filtration media in theopposite direction when subjected to the periodical cleaning fluid andto maintain pleats in the filtration media circumferentially spacedapart at temperatures above approximately 265° F.
 14. The method ofclaim 13 wherein each pleat in the filtration media has a tip and a pairof sides extending from the tip, wherein said applying step furtherincludes the step of providing the retention device to engage at leastone of the tips and sides of the pleats.
 15. The method of claim 13wherein said extruding step further comprises the step of holding androtating the filter cartridge while applying the retention device to thefilter cartridge.
 16. The method of claim 13 wherein the extruding stepfurther includes the step of providing reinforcing structure in theretention device.
 17. The method of claim 13 further including the stepof locating a portion of the retention device between adjacent pleats.18. The method of claim 13 wherein the extruding step further includesthe step of attaching the retention device to the filtration media.